Preparation of polyester yarns having improved heat characteristics



Unite States Patent 3,387,996 PREPARATIGN 0F POLYESTER YARNS HAVENG HMPROVED HEAT CHARACTERiSTiCEs James W. Toiliver, Kinston, N.C., assignor to E. ii. du

Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware N0 Drawing. Filed Aug. 19, 1964, Ser. No. 396,743

2 Claims. ((31. 117-1388) ABSTRACT 01* THE DISCLOSURE An improved polyester yarn is prepared by applying to the yarn a liquid composition of about 0.8 to 1.5 weight percent based on the weight of the yarn, of a liquid coating composition consisting of about 1 to weight percent of certain bisphenols such as 4,4'-thiobis-(3methyl-6-tert-butylphenol) and the remainder (95 to 99%) a diester of the formula R( O-CH CH OR where R is Z-ethylhexoyl and n is an integer from 3 to 7.

This invention relates to improved polyester yarns and, more particularly, to polyester yarns for reinforcement of rubber tires.

In the manufacture of synthetic, continuous-filament yarns, it is necessary for the producer to apply a textiletreating agent to lubricate the yarn and prevent the accumulation of a static charge on the fibers. In the production of reinforced rubber tires, it is desirable, for reasons of efficiency and economy, that the yarns be convertible to cord structures Without any unnecessary intermediate processing. Consequently, the yarn must undergo twisting and hot-stretching operations with minimum strength loss and provide satisfactory performance during the application of the aqueous, adhesive latex. When embedded in rubber, it should promote or, as a minimum, have no deleterious effect upon adhesion, fatigue resistance, flex life, and heat resistance.

Accordingly, it is an object of this invention to provide improved synthetic, continuous-filament yarn for the preparation of cord structures suitable for reinforcing rubber tires. Other objects will be apparent from time to time in the following specification.

This and other objects are attained in accordance with the present discoveries by providing, for the manufacture of tire cord, a polyester yarn to which there has been applied about 0.8 to 1.5 Weight percent based on the weight of the yarn, of a liquid coating composition consisting of about 1 to 5 weight percent of certain bisphenols and the remainder (95 to 99%) a diester of the formula R(O-CH CH OR Where R is 2-ethylhexoyl and n is an integer from 3 to 7. After application of this coating, the yarn is heated, and it is found that the resulting yarn is resistant to degradation of its physical properties in ordinary use for the indicated applications.

It is to be noted that the compositions are liquid and water-insoluble. The bisphenols employed must be soluble in the diester. Insolubility results in a relatively ineffective system. In addition, neither the diester nor the bisphenol used should cause yarn discoloration.

Diesters are, of course, well-known lubricants. Conventionally, such diesters are prepared from dihydric, aliphatic or arylaliphatic alcohols, e.g., 1-6 hexamethylene glycol, p-(hydroxymethyl) phenylethyl alcohol and the like, and, as such, confer no antistatic properties to polyester fibers. For the present invention, it is necessary that the diester be prepared from polyoxyethylene glycols in order that antistatic protection be conveyed to the fibers. Further, it is essential that the polyoxyethylene "ice glycols have a low molecular weight, since too high a molecular weight will result in a water-soluble diester. It has been found that polyoxyethylene glycols having a molecular weight corresponding to 3 to 7 oxyethylene units produce water-insoluble diesters that provide sufficient static protection. As is well-known, the production of ethylene oxide condensates produces a material which is a mixture of various molecular species, and mixtures wherein the average number of ethylene oxide units in the condensate is about 5 are suitable for this invention, that is lubricate and provide adequate antistatic properties. In this respect, antistatic values, as measured by log R should be less than 12.0. Water-soluble diesters are undesirable since they dissolve in the aqueous bath conventionally used to apply adhesive-latex formulations in cord production and utilization. Loss of lubricant not only adversely affects fatigue resistance and flex life, but the accumulation of the material in the bath can seriously impair adhesion when cords from a contaminated bath are subsequently embedded in rubber.

Yarns containing only the above-described diester are deficient in resistance to heat, which, as is wellknown, is developed in tires during use, particularly when run at high speeds for extended periods of time. The addition of about l5% of a bisphenol to the diester, which is soluble in the diester, provides about a 3-fold increase in heat resistance and is, accordingly, an essential feature of this invention. In general, amounts of the bisphenol appreciably less than 1.0% do not provide the desired improvement in heat resistance, while amounts in excess of 5% provide no significantly greater improvement.

Preferred bisphenols are those having the formula I l l X1 X; C (C 113).;

wherein X and X are different and are selected from the group consisting of OH and H, R is selected from the group consisting of H and alkyl groups having 1 to 4 carbon atoms and Y is selected from the group consisting of wherein R is selected from the group consisting of H and alkyl groups having 1 to 3 carbon atoms and I tg CH3 wherein R is H or methyl. As suitable bisphenols, there may be mentioned 4,4-butylidene-bis-(3-methyl-6-tertbutylphenol), 2,2'-methylene-bis-(4-methyl-6-tert-butylphenol), 4,4-(tetramethyl-p-xylylene)-bis-(2,6-di-tert-butylphenol), and 2,2'-thio-bis-( l-methyl-6-tert-butylphenol).

While the amount of the bisphenols in the coating should be between 1.0 and 5% by weight to obtain the benefits of this invention, the optimum amount Will vary somewhat depending upon the particular bisphenol added to the lubricant. The optimum amount will usually be between 2 and 4%. Simple mixing of the bisphenol and diester generally is suflicient to provide the coating composition of this invention.

During the production of polyester yarns, it is necessary to apply heat in order to obtain maximum performance during manufacture and to obtain the desired physical properties. Suitable heating is that normally applied at the draw roll in conventional practice. In practicing this invention, it is essential that yarn carrying a coating of the lubricant not be heated, in the pressure of air, without the bisphenol. Application of diester and bisphenol after heating to give a heat-resistant yarn is less successful than the present invention, as the yarn loses its heat resistance with time, e.g., within five weeks, and a higher bisphenol concentration would be required to achieve a performance equivalent to that of the present invention. In regard to the application of heat, it has been noted that some of the diester is volatilized when the coated yarn is passed over heated rolls. The amount lost will, of course, vary with the yarn speed and roll temperature and may be as much as 2030% of the amount applied and this variation in the actual amount applied relative to that present on the final yarn must be considered.

It has also been observed that the addition of the hisphenols of this invention to the polyester polymer prior to spinning of the polymer to yarn provides improved resistance to heat degradation when the yarn is subsequently coated with the diester. However, such a procedure is less versatile than when the bisphenol is present in the coating since in the latter system only that portion of production to be utilized for the reinforcement of rubber need be treated. Further, this practice is not as efiiective as adding the bisphenol directly to the diester.

While the yarns of this invention may be prepared from any suitable polyester which will provide the proper strength requirements for tire cords, it is preferred that the polyester be polyethylene terephthalate due to the ready availability and relative cheapness of the intermediates. The yarns are prepared by known procedures available to the art in the patent and other technical literature, and will commonly have a denier between 840 and 1260, a tenacity of at least about 9.0 grams per denier, and an elongation of about 13%.

After preparing the polyester yarn as in this invention, the yarn may be twisted and corded in the usual manner for use. Prior to embedding cords prepared from the yarns of this invention in rubber, the cords are treated with an adhesive dip. The dipped cords are then embedded in rubber and adhesion determined by the single and strip adhesion method.

The adhesive dip is applied in two steps. The first step is the application of a blocked isocyanate/epoxide sub coat. In preparing the subcoat, 4.5 grams of sodium di(2- ethylhexyl) sulfosuccinate and 75.0 grams of phenolblocked methylene-bis(4-phenylisocyanate) are added to 220.5 grams of water. The resulting mixture is milled to a fine dispersion and identified as Mixture 1. To 14.4 grams of Mixture 1 dispersed in 84.2 grams of water are added, with stirring, 1.4 grams of a polyepoxide. This dispersion is identified as Mixture 2. The polyepoxide, a glycidyl polyether of glycerol and epichlorohydrin, is prepared as taught in US. Patent 2,902,398 at column 4, lines 1-24. The polyepoxide is a pale yellow, viscous liquid with an epoxide value of 0.67 equivalent per 100 grams and having a molecular weight of about 320 as measured in dioxane solution by the boiling-point-rise method. A polyethylene terephthalate tire cord having an 840-denier, 2-ply (93-tex., 2-ply) construction with 12.0 to 12.5 turns per inch Z-twist in the singles and 12.0 to 12.5 turns per inch S-twist in the ply is dipped in Mixture 2 and heated in an oven for 60 seconds at 218 C. under an applied stretch of about 3% to give a precoated cord having a dried coating pickup of about 1.0% by weight.

The second step is the application of a resorcinol-formaldehyde-latex (RFL) topcoat. Solution 1 is prepared by adding 12.0 grams of aqueous 7.85% sodium hydroxide, 6.9 grams of resorcinol and 10.1 grams of 37% formaldehyde to 139.0 grams of water. Solution 1 is allowed to age at room temperature for six hours and is then added to a mixture of 38.2 grams of water and 152.5 grams of a 41% solids butadiene/styrene/vinylpyridine (70/15/15) copolymer latex to give Mixture A. Mixture A is allowed to age for 24 hours at room temperature. The subcoated cord is dipped in aged Mixture A and heated in an oven for 60 seconds at 218 C. under an applied stretch of about 3%. The dry solid pickup in this step is about.4% by weight, based on the weight of the original cord. The adhesion values reported in Table I are measured by the single end strip adhesion (SESA) method at 25 C. In preparing samples for the SESA test, lengths of treated core are placed in the bottom of a steel mold, the cords being parallel with spacing of 0.5 inch between cords. The cords are placed under dead weight tension to maintain their position. A sheet of unvulcanized natural rubber stock mils in thickness is placed over the cords, covered with a cotton duck reinforcing backing, and the top plate of the mold placed over the backing. The mold is put into a platen press. A pressure of approximately 120 psi. is applied and the mold is heated to about C. for 60 minutes. Due to the flow of the rubber stock, the pressure within the mold falls to a low value during the curing cycle. The specimen is removed from the press while hot and it is found that the cords are firmly embedded in the cured elastomer stock, but are visible on the surface. This sheet is cut into l z-inch wide strips, each having a cord in the center. The cord is separated from the end of the strip; the free end of the elastomer strip so obtained is clamped in the upper jaw of an Instron testing machine and the freed single end of cord in the lower jaw. The machine is then operated to separate the jaws and thereby to strip the cord from the elastomer sheet in a continuous manner. The tension necessary to strip the cord from the elastomer sheet is determined and is reported in pounds tension per single end of cord.

Heat resistance values as reported hereinafter are measured by comparing the breaking strength after heating to the original breaking strength and calculating the percent strength loss. After being drawn and coated, the 840-denier yarn is given 12 turns per inch of Z-twist. Two of the Z-twisted yarns of the same denier are then plied together with 12 turns per inch S-twist. A Z-gram sample of the plied yarn is placed in a dry 30-ml. tube after being desiccated at atmospheric pressure and room temperature overnight. The tube is then sealed under ambient air and heated at 150 C. for 96 hours. The breaking strength of the heated yarn is then determined in the usual manner.

Log R values reported in Table I are determined by measuring the current which flows through a section of a yarn package when a voltage is applied across it. The electrodes are four standard banana-plugs positioned on an insulating base so as to form a 125-inch square. The yarn package, after being conditioned at 21 C. and 65% relative humidity, is placed on the electrodes, voltage of 210 volts is applied and the current flowing through the section of the package bounded by the electrodes is measured. Current measurement is made with a Beckman Model-5 Micro-Micro-Ammeter. The resistance in ohms is calculated. Log R is the common logarithm of the resistance.

EXAMPLE I Yarns of polymer of polyethylene terephthalate, the yarn having a relative viscosity of 51, is melt-spun in a known manner to give a 192-filarnent yarn. As a processing aid a solution of about 23 parts by weight of a diester as in this invention and 77 parts of refined kerosene is applied to the yarn shortly after the quenched filaments are converged to a bundle.

The unoriented, spun yarn is hot-drawn at a draw ratio of 6.1., by passing the yarn through a steam jet positioned between an unheated feed roll and a draw roll heated to C. to give a yarn having a drawn denier of 840. In the jet, superheated steam at a temperature 375 C. is impinged, at a high velocity, upon the yarn to heat it to drawing temperature. The superheated steam removes essentially all of this kerosene-containing solution from the yarn, there being less than 0.05% by weight remaining on the yarn. Between the jet and the draw roll, there is applied to the yarn a coating solution consisting of 98% of the di(2-ethylhexanoate) of a mixture of polyethylene glycols having an average molecular weight of about 238 and 2% of 4,4'-thio-bis-(3-methyl- 6-tert-butylphenol), and the yarn is then collected as Sample A.

A second run is made identical to A except that the yarn coating contains no 4,4'-thio-bis-(3-methyl-6-tertbutylphenol). This yarn is identified as Sample B.

A third sample of yarn, C, is prepared in similar fashion to that of yarns A and B except that the draw roll is heated The data in Table II clearly show the need to heat the yarn immediately after application of the liquid coating to obtain the full benefit of the present discovery.

The foregoing discussion and description demonstrate the advantage of the coating composition of the present invention. It should be appreciated that variations from the detailed embodiments can be made without departing from the scope of this invention.

What is claimed is:

1. In the process of producing polyester yarn for applito 100 C. Sample C is given a post-draw application of a lo cation as tire cord in which a finish is applied to the composition consisting of 54 parts by weight of butyl yarn, the improvement comprising applying as said stearate, parts by weight of sorbitan monolaurate, finish a liquid composition consisting of about one to and 31 parts by weight of a refined kerosene. A fourth five percent by weight of a compound of the formula sample is prepared by extracting a portion of Sample B 15 R1 R! six times with carbon tetrachloride and identified as Sample D.

The yarns are then subjected to the previously described I I procedures, with the results shown in Table I. C(GI-Im X, X1 C(OHm TABLE I Elon- Percent Adhesion Breaking Strength (lbs) Strength Sample Tenacity gation Finish Log IR Less gJd.) (percent) on Yarn No 2-week Before After (percent) Lag Lag Heating Heating A 0.4 12.8 1.1 11.6 3.0 2.7 28.3 22.4 B 0.1 12.0 1.2 11.7 3.0 2.4 20.0 12.2 50 C 9.2 11.6 1.2 10.4 2.8 1.2 28.0 14.0 50 1) 9.2 12.6 0 30.3 25.1 t

1 Typical values.

2 Average of two measurements.

In all other important aspects, e.g., hot-stretching performance, fatigue life, etc., yarns A, B, and C are considered to be equivalent.

From these results it will be noted that the yarns of this invention provide a markedly superior resistance to heat compared with those treated with other coating compositions. The two-week lag designation in Table I refers to the practice of storing the yarn between subcoat and topcoat application. The advantage shown by the yarns of this invention in this respect is important since all cord processors are not equipped to handle a continuous double-dip application necessitating lagging prior to topcoat application.

EXAMPLE II A polyethylene terephthalate yarn is prepared as described for Sample A of Example I except for the postdraw application of the coating composition. Yarn so prepared contains about 0.04% by weight of the kerosenecontaining finish, based on the Weight of the yarn. The coating solution used in the post-draw application to Sample A is then applied to this yarn by passing it over a roll partially immersed in the coating solution and the yarn picks up 1.2% by Weight of the coating composition, based on the weight of the yarn. This yarn is identified as Sample E and it differs from Sample A essentially in that it is not heated (e.g., by a draw roll) immediately after application of the coating. The heat resistance of Sample E and Sample A is measured, as previously described, at intervals after preparation. The results are where X and X are different and are selected from the group consisting of OH and H, R is selected from the group consisting of H and alkyl groups having 1 to 4 carbon atoms, and Y is selected from the group consisting of wherein R is from the group consisting of H, alkyl groups having 1 to 3 carbon atoms and i -z Illa where R is of the group consisting of H and methyl, and the remainder a compound of the formula R( O-CH CH ,,OR

where R is 2-ethylhexoyl and n is an integer from three to seven and thereafter immediately heating the coated yarn.

2. A product prepared by the process of claim 1.

References Cited UNITED STATES PATENTS 2,920,980 1/1960 Mooberry 117138.8 2,993,811 7/1961 Smith et a1 117138.8

FOREIGN PATENTS 959,325 5/ 1964 Great Britain.

WILLIAM D. MARTIN, Primary Examiner,

R. HUSACK, Assistant Examiner. 

